[Xen-devel] Occasional clock/time problems on HVM domU after live migrate on Xen 4.2.{1, 2}

[Alex Bligh <alex@xxxxxxxxxxx>]

I am seeing occasional clock/time problems on an HVM domU with upstream 
qemu-dm on Xen 4.2 (more precisely 4.2.2-rc1 with my live migrate
patches).

I'm migrating between two machines with identical hardware. I'm using an
Ubuntu Precise dom0 and domU. The machines run ntp in dom0 for what its
worth, but their RTCs may not be synced.

When I migrate a machine in one direction it very frequently works. However,
sometimes, executing a ping command on the migrated machine appears to fail.
Close inspection suggests the networking works (I can see traffic going in
and out), but the machine's idea of time is all screwed up so ping gets
confused into sending nothing. It's as if time is not moving forward on
the migrated machine.

Possibly for a similar reason, the paravirtualised domU vNIC which is
attached to a bridge in dom0 sometimes comes up 'NO CARRIER' for no
discernable reason. It appears to be a member of the relevant bridge
according to brctl. I'm not sure how the pv nic detects the presence
of 'carrier'.

Any ideas?

--
Alex Bligh

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